Five studies are proposed to explore the effects of drug preloads on drug craving and likelihood of drug self-administration in humans. The first three studies will evaluate the effects of tobacco smoke, other drugs and smoking-related stimuli in temporarily abstinent cigarette smokers. The next two studies will assess the effects of an ethanol or other-drug preload on the likelihood of choosing ethanol over a placebo, using an in-house preference procedure. Subjects for these studies will be normal (non-problem) social drinkers. The last study will explore the effects of pretreatment with amphetamine on preference for amphetamine using an out-patient preference procedure in normal volunteers. We wish to evaluate the hypothesis that ingestion of a positively reinforcing and/or formerly self-administered drug increases ratings of drug craving as well as drug-seeking behavior.